In the summer of 1940, the question Britain asked itself was not 'will Hitler invade?' but 'when?'. Operation Sealion, the German invasion plan of Britain, provoked the construction of pillboxes, anti-tank stop-lines and islands, coastal defences, heavy-gun emplacements and anti-aircraft batteries, as well as the formation of the Home Guard and covert groups. As the threat of invasion passed other threats emerged. These years saw the expansion of the British radar detection systems during the Blitz years, as well as, intelligence-gathering systems and listening posts. In 1944 and 1945, Britain was once again faced with a new and deadly threat, Hitler's 'Vengeance weapons'. This book provides a concise assessment of Britain's defensive systems, and presents a vivid picture of war on the home front. Text by Bernard Lowry with illustrations by Chris Taylor and Vincent Boulanger.